Currently, locks are known which are adapted for example to allow the closure and re-opening of a door or gate and comprise a preset cylinder which can be actuated by means of a suitable key which can be inserted in a keyhole provided axially to this cylinder.
These cylinders of the known type are typically made of brass and therefore do not have a high mechanical strength, being thus easy to break into by drilling and/or breaking and/or stripping.
In order to protect these cylinders of the known type from possible break-ins, it is common to fix to the lock, in such a position as to cover the cylinder, an adapted covering element, which is constituted by a stud which has a substantially circular plan shape and has, at the keyhole of the cylinder, a circular hole inside which a keyhole protection disk, in which there is a slot adapted to allow the insertion of the key, is accommodated rotatably.
The stud constitutes therefore a protection for the cylinder and allows at the same time the insertion and rotation of the key in the keyhole thereof.
These studs of a known type, however, have a drawback: in fact, even after their application the cylinder is partially accessible through the slot of the keyhole protection disk and therefore is still vulnerable to possible tampering or vandalism, such as for example, the introduction of glue or other substances that could damage the cylinder through this slot.
As a partial solution to this drawback, patent application no. TV2003A000115 of Aug. 7, 2003, is known which describes a protective device for the cylinder of a lock which comprises a plate, with an approximately rectangular plan shape, which can be fixed to a door so as to cover the lock, and can be provided, proximate to one end, with a suitable opening for access to the cylinder of said lock.
On the front surface of the plate, which is directed opposite to the lock, there are two adapted seats having a circular plan shape within which two substantially cylindrical cams are accommodated so that they can rotate, two recesses with a semicircular profile being formed radially on their lateral surface; adapted first magnets are inserted within said cams.
Two through ducts are provided on the lateral surface of these seats, along two axes which are transverse to the plate, and suitable lock pins are accommodated within said ducts so that they can slide, said pins having such dimensions as to be partially insertable in the recesses formed in the cams; these pins are pushed toward the outside of the respective ducts, so as to exit transversely from the lateral surfaces of the plate, by the action of adapted springs inserted in said ducts.
A covering element is associated slidingly with the plate and can slide longitudinally thereto, so as to conceal selectively, with one of its ends, the opening for access to the lock.
This covering element has an approximately C-shaped transverse cross-section so as to define a substantially rectangular base arranged, when in use, so as to face the front surface of the plate; two arms protrude from the longitudinal ends of said base, envelop the lateral surfaces of the plate and are slidingly coupled thereto.
Two adapted slots are formed in the surface of said arms that is directed toward the longitudinal surfaces of the plate; in the condition in which the covering element conceals completely the opening for accessing the lock, the pins that protrude transversely from the lateral surfaces of the plate are inserted in said slots so as to block the mutual sliding between the plate and the covering element.
The release of the covering element is achieved by arranging in a complementarily shaped groove formed in the base thereof an adapted magnetic key which contains preset second magnets adapted to mate with the first magnets provided in the cams, in order to cause the rotation of said cams up to the condition in which the recesses formed in them face the channels that contain the pins.
In this condition, a traction of the covering element in the direction of its spacing from the opening for accessing the lock causes the exit of the pins from the cavities formed in the arms of said covering element and the simultaneous partial insertion of said pins in the recesses of the cams; in this manner, the sliding of the covering element with respect to the plate is freed, thus allowing access to the lock.
Once the magnetic key has been removed and the covering element has been repositioned so as to conceal the opening for accessing the lock, the mutual interaction between the first magnets of the two cams causes a rotation thereof such as to break up the alignment of the recesses with respect to the ducts that contain the pins; the covering element is therefore again locked in a closed condition.
However, even this device of a known type has some drawbacks: in fact in disk combination systems, because of the mechanical plays between the various components and because of the different sounds that the disks produce upon contact therewith depending on their mutual position, it is possible, after various listening attempts, to detect the opening position of all the disks and therefore open the lock.
Italian patent no. 01288200 is also known which describes a safety device for the protection of the external side of a system for closing doors or door-frames for entry, which comprises a fixed base element, which is arranged and shaped to surround a locking cylinder, i.e., the hole for the key of the closing system.
In front of the base element there is a longitudinal seat, with two parallel sides, in which a movable body is accommodated so that it can slide; said body can be moved between an active position, in which said movable body is arranged in front of the cylinder, i.e., of the lock hole, concealing it, and a passive position, in which said movable body is spaced from the cylinder, i.e., from the lock hole, so as to allow access thereto.
The device comprises, moreover, a combination system for locking/unlocking the movable body in the active position, constituted by rotating coded knobs which are mounted on the movable body, each one carrying a lock/unlock disk, arranged on the inner face of the movable body, between the sides of the front seat of the base element; on these sides, for each one of the disks, there is a recess which is partially shaped complementarily, in plan view, to the respective disk and is arranged so that when the movable body is in the active position each disk is arranged proximate to one of said recesses.
Each disk, moreover, has a lateral flattened portion, which can be arranged selectively, following the rotation of the disk, at the respective recess or not; with the movable body in the active position, when the flattened portion of a disk is not at the recess, said disk protrudes transversely from the movable body with its curved part, which is thus arranged inside the adjacent recess, preventing the sliding of the movable body with respect to the base element and thus keeping said movable body in the active position.
By rotating in a suitable manner the coded knobs it is possible to rotate the disks until the flattened portion that is present in all of them is at the respective recess; in this condition, the disks do not protrude transversely from the movable body, which is no longer coupled to the base element and can therefore be caused to slide to the passive position.
The release of the movable body is therefore possible only by knowing the correct combination that makes it possible to rotate conveniently the coded knobs and the lock/unlock disks with them.
Even this device of the known type, however, has drawbacks: in fact it is known that in disk combination systems, because of the mechanical plays between the various components, and due to the different sounds that the disks produce upon contact with them depending on their mutual position, it is possible, after various listening attempts, to determine the open position of all the disks and therefore open the lock.
Moreover, in this device of the known type, the position of the coded knobs that makes it possible to achieve the release of the movable body is not defined unequivocally, because in order to achieve the release of the movable body it is sufficient for all the disks to be arranged so that their flattened portion is partially contained in the recess and directed away from the locking cylinder or hole for the key of the closing system; in fact in this condition, which can be obtained with the coded knobs in various positions, by pulling of the movable body in the opening direction the flattened portion of the various disks abuts against the edge of the respective recess, causing the rotation of the respective disk up to the condition in which the curved portion thereof completely protrudes from the recess, thus releasing the sliding of the movable body.
Moreover, this device of the known type has a further drawback: as also observed previously, when the movable body is in the passive position the coded knobs are arranged necessarily so as to define the opening combination; in order to prevent someone from being able to read this combination in this condition it is therefore necessary, after each use, to return the movable body to the passive condition and rotate the coded knobs in order to achieve the locking of said movable body, and this may be inconvenient.
Italian application no. VE2007A000070 dated Oct. 3, 2007, is also known which claims a protective device, particularly for a lock of a door or leaf, which comprises a covering element associated slidingly with a plate which can be fixed to said door or leaf and can be arranged selectively so as to close an opening, for accessing said lock, which is formed in said plate, at least two pins being associated transversely with said plate and cooperating with cams accommodated rotatably within said plate and adapted to block temporarily the sliding of said covering element with respect to said plate, characterized in that said cams interact with a magnet-based combination element adapted to modify the angular position of said cams in order to allow or prevent the temporary mutual release of said pins and said covering element.
Even this solution has drawbacks, because the thief might still detect, by listening to the movement of the cams, their position and achieve the condition for disengaging the pins.